This invention relates to improvements in self-interference mitigation in two-way relayed communications, particularly as implemented through a satellite link.
Self-interference cancellation is a theoretically efficient technique for removing interference on a channel containing a remote signal and a near signal in relayed communication between two or more devices involving the transmission of different signals within the same frequency band at the same time. In the example of communication between two devices, such transmission results in a composite signal that includes two signals, one originating from each device. As each device attempts to receive the signal originating from the other device (remote signal), it is hindered by interference caused by the signal originating from itself (near signal). Self-interference removal techniques are used to remove the unwanted near signal wherein the local device typically generates a “cancellation signal” resembling the device's own near signal and then uses the cancellation signal to remove at least a portion of the near signal from the composite signal to obtain a signal closer to the desired remote signal.
A number of representative techniques addressing to the general problem have been disclosed in U.S. Pat. Nos. 5,596,439 and 6,011,952, both issued to Dankberg et al., U.S. Pat. No. 5,280,537 issued to Sugiyama et al., U.S. Pat. No. 5,625,640 issued to Palmer et al., U.S. Pat. No. 5,860,057 issued to Ishida et al., and described in U.S. patent application Ser. Nos. 09/925,410 and 10/006,534 assigned to the assignee of the present application. Known self-interference removal techniques are limited in that there are uncompensated—for imperfections in the subsystems, such as the upconverter and downconverter stages, leaving room for improvement.